1. Field
The following description relates to creation and editing of content, and more particularly, a technology for creating and editing a 3-dimensional virtual character animation.
2. Description of Related Art
3-dimensional virtual characters have been widely used in a range of digital content, such as movies, games, broadcasting, and avatars. And it is generally understood that in order to create animation wherein a virtual characters exhibit realistic movements, both, quantitative and qualitative aspects need to be considered.
The quantitative aspects of the character animation, such as location, velocity, and acceleration of motion, can be numerically calculated, while in many cases, the qualitative aspects are difficult or impossible to numerically analyze. Especially, when a new motion generated by editing the qualitative aspects of a particular motion, timing that indicates the start and end of said motion plays a key role in expressing the motion style and characteristics. For example, if a motion of a character moving from one location to another has faster timing, it may appear to be energetic and dynamic, whereas even the same motion that has slower timing may appear to be tired and depressed. Also, if a character is stationary at the same position for a long period of time, the character's motion appears to have discontinuities between movements. On the contrary, a short motion sequence in which the character is stationary makes the overall movements in the motion look organic and smooth. Therefore, in the process of editing a motion style by using an articulated skeleton model, which consists of multiple joints and is widely used in generating character animation, the user needs to adjust as many joint rotation timings as the number of joints.
A popular method being used for generating character motions is key-frame animation, which has been widely used. In this method, the user is allowed to freely generate a motion of a desired style, but editing a number of motion timings that correspond to key frames is a laborious and time-consuming task for the following reasons:
First, the multi joint skeleton model has high of degrees of freedom (DOF) and the user is required to have specialized training and physical knowledge about human movements (e.g., constraints imposed on a range of human movements due to the gravity and shift correlations between joints) in order to generate a motion that is of a high quality by adjusting the timings associated with a number of joints. It is especially difficult for a user to express a realistic shift of weight and kinetic energy, which is closely connected to character motion timings, if said user is one who lacks experience and expertise in editing the temporal aspects of motion.
Also, 24 to 30 or more frames of postures in a motion need to be generated per second in order for the character animation to look natural. To this end, editing timings of all joints that relate to key postures is required, and this task is time consuming even to experienced animators.
Finally, most commercial 3D modeling tools for editing motion timing use a complicated editing process and user interface, and hence it is, indeed, difficult for a novice user to generate realistic and natural animation using such tools. For the above reasons, the key-frame animation technique requires a large number of skilled animators to make even a short character animation if it is of a high quality, resulting in an increase of production cost.
Meanwhile, another method for generating character motions is motion-capturing, whereby movements of a performer are recognized and tracked, in real time, via a number of cameras, and then the movements are reconstructed as motions of a virtual character model. In this method, the movements of the performer are directly recorded, so that it is possible to generate motion data that is of a very high quality. Especially, the captured 3D motion data is fitted onto a multi-joint skeleton, and thus can be easily applied to the existing character animation production pipeline. However, 24 to 30 or more frames per second for a motion are captured according to the speed of a camera, and thus the generated motion data has high level of continuity and density between frames. As a result, when editing timing information in the captured data, the user may unexpectedly destroy physical validity of movements in the consecutive frames. Accordingly, when the user transforms the captured data into a desired motion style, the results may exhibit a lesser quality due to unnatural movements and noise. Also, a high-quality motion capture system for recognizing and tracking motion data is a very costly equipment, which requires an enough physical space for motion capturing and a number of operators with specialized training. In particular, the proficiency of the performer for the motion capturing is the factor that is most influential to motion quality; for example, it is quite difficult to extract high quality of timing information of complex, dynamic motions, such as dance and athletics, from movements of an ordinary person, which is the reason a professional performer would be needed. For the aforesaid reasons, generation of motion data via motion capturing requires quite a long preparation time and high cost.